A ROT13 converter script for fonts.
You will need fontforge to run font13.py:
$ fontforge -script font13.py font.ttf
Example:
$ sudo apt install fontforge
$ fontforge --version
...
Version: 20190801
...
$ wget --content-disposition https://fonts.google.com/download?family=Roboto
$ unzip Roboto.zip Roboto-Regular.ttf
$ ls -1 Roboto-Regular.ttf
Roboto-Regular.ttf
$ fontforge -script font13.py Roboto-Regular.ttf
$ ls -1 Roboto-Regular.ttf Ebobgb-Erthyne.ttf
Roboto-Regular.ttf
Ebobgb-Erthyne.ttf
$ cp Roboto-Regular.ttf Ebobgb-Erthyne.ttf ~/.fonts
$ pango-view --font Roboto --text 'The quick brown fox jumps over the lazy dog' --waterfall
$ pango-view --font Ebobgb --text 'The quick brown fox jumps over the lazy dog' --waterfall
$ pango-view --font Roboto --text 'abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ' --waterfall
$ pango-view --font Ebobgb --text 'abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ' --waterfall